The process of making paper involves harvesting fibers from plants, typically trees, through a pulping process that separates the plant material into individual fibers. The resulting pulp fibers are diluted with 200 parts of water to one part fiber by weight. This fiber suspension, now referred to as stock, is supplied to a paper machine through a head box, which spreads the stock onto a moving wire to begin the process of de-watering the stock and consolidating the fibers into a formed paper sheet.
As water is drained from the forming sheet, individual fibers that were once relatively free to move independently become immobilized in a network of cellulose fibers held together by hydrogen bonding between the water and cellulose molecules. Water is then removed from the resulting sheet by mechanical pressing and then by drying until the finished sheet of paper is produced.
The production of paper has become more reliant on pulp that has been derived from waste paper recycled from many sources. Normally, recycled paper pulp is combined with un-recycled pulp to improve the quality of the resulting paper and to compensate for damage to the fibers of the recycled pulp that may occur during the recycling process. The large variation in the quality of recycled pulp effectively limits the amount of recycled pulp that may be added to the stock if a given paper quality is to be assured.